As electric signals have higher frequencies, Low Temperature Co-fired Ceramic (LTCC) substrates have been widely used. The LTCC substrates are substrates made of LTCC for which a metal material having a low conductor resistance can be used and which can be fired at a low temperature of less than or equal to 1000° C. LTCC stands for Low Temperature Co-fired Ceramic. An LTCC substrate is formed by providing a via for conduction within a via hole processed in a green sheet thereof, stacking a plurality of the green sheets provided with the vias, and co-firing a ceramic material constituting the green sheets and a conductor material constituting the vias. Thereby, a high-density multilayer substrate can be formed at low cost. Since LTCC has a dielectric constant of more than or equal to about 5 and less than or equal to about 7, and passive elements such as a resistor and a capacitor can be embedded therein, it is suitable for use in high frequency digital applications.
Here, a case of forming a module in which an LTCC substrate is used to seal a power device or a MEMS (Micro Electro Mechanical Systems) structural body is considered. On this occasion, there is a case where an LTCC substrate is used to seal a device formed on a silicon substrate, and the LTCC substrate is provided with a cavity for storing the device, as described for example in Japanese Patent Laying-Open No. 2013-30759 (PTD 1). Further, there is also a case where a cavity is formed in an LTCC stacked substrate and a chip component is mounted within the cavity, as described for example in Japanese Patent Laying-Open No. 2010-283074 (PTD 2).